Uses:
A hydrocarbon is an organic compound consisting
entirely of hydrogen and carbon. The hydrocarbons are the most broadly used
organic compounds known, and are quite literally the driving force of western
civilization. The greatest amounts of hydrocarbons are used as fuel for
combustion, particularly in heating and motor fuel applications. The primary
components of natural gas are methane and ethane. We are all familiar with the
use of propane in gas barbecues, lanterns, and as a fuel for internal
combustion engines and heating systems. Butane is also a readily available
fuel, familiar to everyone in the form of the pocket lighter.
With pentane, the saturated hydrocarbons enter the realm of
room-temperature liquids. This makes them useful as organic solvents, cleaners,
and transport fuels. Petrol (Gasoline) for internal combustion engines in cars, trucks,
tractors, lawnmowers, and so on, is rated in combustion properties relative to
octane. It is in fact a combination of liquid hydrocarbons ranging from hexanes
to decanes. Slightly larger hydrocarbons are known as kerosene or jet fuel,
diesel fuel and heating oil. Still larger hydrocarbon molecules serve as
lubricating oils, and greases. Eventually a point is reached at which the
materials are solids at room temperature. These are the waxes. Hydrocarbon
molecules larger than those of the waxes are the heavy greases and the tars
commonly used in roofing applications and highway construction.
Most
hydrocarbons are generated from the thermal 'cracking' and fractional
distillation of crude oil. Another major source is the industrial alteration of
ethanol to produce ethylene. The ethylene so produced becomes a feedstock for
the industrial synthesis of other hydrocarbons up to and including
polyethylene.
Problems:
Environmental Problems Associated With the Combustion
of Hydrocarbons
Hydrocarbons are burned, or
combusted, primarily in engines, power plants and heating systems. Known more
commonly as fossil fuels, the hydrocarbons humans burn are coal, natural gas
and petroleum products. If combustion were 100 percent efficient and all
hydrocarbons contained only hydrogen and carbon, the sole byproducts would be
water and carbon dioxide. There are unintended waste products, however, and
they cause environmental harm. Even carbon dioxide, which is a natural part of
the atmosphere, becomes a pollutant when released in excessive amounts. The
environmental liabilities associated with hydrocarbons provide incentives for
the development of alternative energy sources.
Polycyclic
Aromatic Hydrocarbons
The
incomplete combustion of hydrocarbons, especially coal and diesel fuel, causes
the release of altered hydrocarbons. These hydrocarbon pollutants, known
collectively as polycyclic aromatic hydrocarbons, take a variety of forms. Some
are quite toxic, known to harm aquatic life and cause cancer.
Oxides
of Carbon, Nitrogen and Sulphur
Incomplete
combustion of hydrocarbons also results in carbon monoxide pollution. An
odorless, colorless gas, carbon monoxide causes headaches and complications for
people with heart disease. Carbon dioxide is always released when hydrocarbons
are burned. It is a leading cause of global climate change and the
acidification of oceans. Combustion of oil and coal, in particular, causes the
release of nitrogen oxides and sulfur dioxide. These oxides combine with water
and oxygen in the atmosphere, creating nitric and sulfuric acids, which return
to Earth's surface as acid deposition, or "acid rain." Acid
deposition harms aquatic organisms and kills trees. Because it makes certain
nutrients, such as calcium and phosphorus, less available to plants, it reduces
the productivity of ecosystems and farms. An additional problem associated with
nitrogen oxides is that they, along with hydrocarbon pollutants, contribute to
the formation of tropospheric ozone, a major component of smog.